Present day communications technology is directed more and more to the use of optical fibers for transmission and hence the use of optical fiber cables containing a plurality of coated or sleeved optical fibers. The cables may take any of a number of forms such as a plurality of fibers contained within a tubular protective member, thereby forming a core or bundled together in protective loose tubes surrounding a central strength member. Alternatively, the fibers may be arrayed side by side on a ribbon member, with a plurality of such ribbons being stacked to form a high fiber count cable, and which are then enclosed in a protective plastic tube or jacket. Regardless of the type of cable used, splices are necessary for joining the ends of cables, and the fibers contained within them. It is necessary, therefore to enclose the splices in a closure to contain and protect the splices of two or more fiber optic cables.
Glass optical fibers are of extremely small diameter and are relatively fragile, therefore, optical fibers must be treated more carefully in placing them and their splices, within an enclosure. The closure must anchor all cables stored within, and it must be capable of withstanding torsional and axial loads transmitted by the cable to the closure so that the splices are protected from these loads. The closure must also seal the inner and outer sheaths of the cables and maintain the seal integrity under extreme environmental conditions. The sealing must also provide a moisture barrier sufficient to prevent any moisture from reaching the fiber optic splices.
Increasingly there has been a demand that closures be supplied with the necessary components included in one package, thereby relieving the customer of the necessity of "customizing" his particular closure with the required components, and it has become a desideratum in the optical fiber splice closure art that the components necessary to complete the closure, such as the fiber splitter for routing fibers, the splice trays for holding the splices, a grip assembly for anchoring the cables entering and leaving the closure, a ground assembly for grounding the metallic strength members, and an overall protective cover for protecting the fiber optic splices contained within the closure which can be quickly mounted or removed, be capable of universal application, thereby accommodating virtually any size of cable within a specified range of cable sizes and any type of splice.
In U.S. Pat. No. 5,862,290 of Burek et al. there is shown a splice closure which meets the foregoing criteria, which is referred to as the 3000 type closure. More particularly, the patent also discloses the numerous individual components of the closure which make possible meeting of these criteria. Among these components there is shown a grip block assembly which anchors incoming and outgoing cables to the closure member. The grip block assembly comprises a lower grip member having first and second pivoted arms and an upper grip member having first and second actuating pins for actuating the pivoting arms into gripping contact with the cable. When the upper and lower grip members are tightened by means of a bolt or bolts, the cable is gripped firmly and remains, during use, substantially stationary to the housing. The terms "upper" and "lower" are not meant to indicate the position of the part in use. As will be seen hereinafter, the parts may be inverted in use, whereby the "upper" part becomes the actual lower part, and vice versa.
The cable grip assembly of that patent is such that it grips a single cable of any one of a number of diameters. However, with increased capacity of the splice closure being a principal desideratum, it becomes necessary to use some other form of grip block capable of anchoring two cables, or affording a wider range of diameters for single cables, which are both sealed using side entry, sealing ribs, eccentric shaped insert grommets.
In order to insure protection of the splices from moisture, it is current practice to form the closure out of two mating halves, with a grommet therebetween, and clamp them together. Cable entry is through openings in the grommet, which are usually supplied with inserts which seal the cable and in turn are sealed by the grommet. Such a grommet and insert arrangement is shown, for example, in U.S. Pat. No. 5,472,160 of Burek et al. In that arrangement, the grommet, which is of a resilient material suitable for moisture sealing has, at each end thereof, first and second seal members having bores therein for receiving grommet inserts which in turn have bores therein for receiving the cable. The seal members are preferably split longitudinally so that the grommet inserts, with cables extending therethrough, can be inserted in the seal member and be tightly embraced thereby. When the two halves of the housing are clamped together, the cable is tightly embraced, as are the seal member, so that a watertight seal is achieved.
In usage, it has been found that such a sealing arrangement can be vulnerable to a bending or flexing of the cable adjacent the entrance to or exit from the closure which can, in some instances, break the integrity of the seal. There have been various arrangements in the prior art for correcting this effect, one such arrangement being shown in U.S. Pat. No. 5,434,945 of Burek et al., wherein the closure is encased in a protective shell. Such an arrangement insures that the splice closure itself is virtually certain to be moisture proof.
In U.S. Pat. No. 5,862,290 of Burek et al. the foregoing sealing problem is addressed by the provision of two sealing inserts for each cable entrant or exit port which are butted together longitudinally in end to end relationship and which contain the fiber containing cables. The use of two inserts per cable is meant to insure against unseating of the inserts as a result of external flexing forces on the cable. These forces are absorbed by the outer insert while the inner insert remains unaffected, hence sealed. In this way external flexing forces do not destroy the integrity of the seal of at least one insert in each entry port. However, it has been found that there are sometimes extreme forces on the cable which might result in the unsealing of both inserts in the entry (or exit) port, such as a high degree of bending stress for large cables.
Thus, it can be appreciated that there is a need for a more versatile or universal grip block for use with a splice closure that is capable of immobilizing more than just one cable, as well as an arrangement for enhancing or insuring seal integrity at the cable entrance or exit port.